1. Field of the Invention
The present invention relates to an injection molding machine and, more particularly, to the centering of a nozzle hole formed in an injection nozzle to a sprue hole formed in a mold.
2. Description of the Related Art
An injection molding machine seats the injection nozzle of an injection unit against the sprue bushing of a mold mounted on a stationary platen and injects melted resin from a nozzle hole in the injection nozzle into the mold through a sprue hole provided in the sprue bushing. The central axis of the sprue hole must accordingly be aligned with the central axis of the nozzle hole in the injection nozzle; this involves a process of centering the nozzle hole in the injection nozzle to the sprue hole in the mold and adjusting the centering.
In conventional nozzle hole centering, it is known art to mount a ring-shaped member at the end of the injection nozzle and insert the ring-shaped member into the injection nozzle insertion opening in the mold by moving the injection unit while visually monitoring interference between the ring-shaped member and the injection nozzle insertion opening, thereby centering the nozzle hole, or to detect the injection nozzle insertion opening in the mold with an optical sensor attached at the end of the injection nozzle, thereby centering the nozzle hole (see Japanese Patent Application Laid-Open No. 09-11277).
It is also known art to configure an injection nozzle alignment jig by providing a mirror section at the center of the stationary platen on the side facing the injection unit, opposite to the side on which the mold is mounted; a light source emitting a laser beam toward the injection nozzle is disposed in a hole formed at the center of the mirror section; the reflection of the injection nozzle in the mirror section is monitored and the injection apparatus is moved horizontally and vertically by operating adjustment bolts so that the laser beam passes through the hole in the injection nozzle, thereby centering the nozzle hole (see Japanese Patent Application Laid-Open No. 11-342523).
It is also known art to image the injection nozzle and the inlet bushing on the mold with a camera, measure the displacement between the central axis position of the imaged injection nozzle and the position of the imaged inlet bushing, and make centering adjustments accordingly (Japanese Patent Application Laid-Open No. 2001-225373).
In conventional injection nozzle centering methods, alignment with the sprue hole is generally carried out while the injection nozzle position or the position of another part is observed visually. In the method disclosed in the above Japanese Patent Application Laid-Open No. 09-11277, for example, the injection nozzle position is visually observed. The task of bringing the nozzle hole and the sprue hole into contact with each other and checking the amount of displacement has to be repeated through a trial-and-error process. In addition, when observing the injection nozzle directly, the operator has to bring his or her face close to the injection nozzle and injection cylinder, which are at high temperatures. In the invention described in the above Japanese Patent Application Laid-Open No. 11-342523, in which the centering adjustment is made while the reflection of the injection nozzle in the mirror is being visually monitored, the operator also has to bring his or her face close to the injection nozzle and injection cylinder, which are at high temperatures. Another problem raised by visual adjustment is that the displacement and the direction of adjustment are not quantitative and thus a trial-and-error process has to be repeated.
The method described in the above Japanese Patent Application Laid-Open No. 2001/225373, in which a camera is used, requires that the jig and camera be placed in the central axis direction of the nozzle hole. Space to accommodate the jig and camera is then required between the injection nozzle and sprue. After the central axis of the nozzle hole and the central axis of the sprue hole have been aligned, therefore, the injection section has to be moved over a considerable distance to actually bring the injection nozzle and the mold into mutual contact; if the injection section cannot be moved straight forward with high accuracy, a displacement may be produced between the central axis of the nozzle hole and the central axis of the sprue hole when the injection nozzle comes into contact with the mold. Extra work is also required to mount and then detach the jig so that the injection nozzle can be brought into contact with the mold. Obtaining enough space between the injection nozzle and the sprue is also problematic: to form the space, the injection section must be capable of moving over a sufficiently long distance in the central axis direction of the nozzle hole, making the machine large.